Virtualization

    

Virtualization
Virtualization allows multiple operating system instances
to run concurrently on a single computer, it is a means of
separating hardware from a single operating systems.
Virtualization uses specialized software designed to allow
multiple operating systems to run concurrently. Each
Virtual Server act like a unique physical device, capable of
running its own operating system
Why use Virtualization ?
Consolidation
Redundancy
Legacy Hardware
Migration
Segregation
Consolidation
It is a common practice to dedicate each server to a single application. If several
applications only use a small amount of processing power, the network administrator can
combine several machines into one server running multiple virtual environments. For
companies that have hundreds or thousands of servers, the need for physical space can
decrease significantly.
This saves on:
•Cost : 10000$ per maintenance cost per machine
•Space: Less servers, less space needed
•Energy: Savings by upto 80%
•Environment: Reduced CO2 emissions due to decrease in number of servers
Redundancy
Server virtualization provides a way for companies to practice
redundancy without purchasing additional hardware. Redundancy
refers to running the same application on multiple servers. It's a
safety measure -- if a server fails for any reason, another server
running the same application can take its place.
This minimizes any interruption in service. It wouldn't make sense
to build two virtual servers performing the same application on the
same physical server. If the physical server were to crash, both
virtual servers would also fail. Inmost cases, network
administrators will create redundant virtual servers on different
physical machines.
Segregation
Virtual servers offer programmers isolated, independent systems in
which they can test new applications or operating systems. Rather
than buying a dedicated physical machine, the network
administrator can create a virtual server on an existing machine.
Because each virtual server is independent in relation to all the
other servers, programmers can run software without worrying
about affecting other applications
Legacy Hardware
Server hardware will eventually become obsolete, and switching
from one system to another can be difficult. In order to continue
offering the services provided by these outdated systems – some
times called legacy systems -- a network administrator could create
a virtual version of the hardware on modern servers. From an
application perspective, nothing has changed. The programs
perform as if they were still running on the old hardware. This can
give the company time to transition to new processes without
worrying about hardware failures, particularly if the company that
produced the legacy hardware no longer exists and can't fix broken
equipment.
Migration
An emerging trend in server virtualization is called migration.
Migration refers to moving a server environment from one place to
another. With the right hardware and software, it's possible to
move a virtual server from one physical machine in a network to
another. Originally, this was possible only if both physical machines
ran on the same hardware, operating system and processor. It's
possible now to migrate virtual servers from one physical machine
to another even if both machines have different processors, but
only if the processors come from the same manufacturer
Web Server
Windows
IIS
App Server
Linux
Samba
DB Server
Linux
MySQL
EMail
Windows
Exchange
The Traditional Server Concept
And if something goes wrong ...
Web Server
Windows
IIS
App Server
DOWN!
DB Server
Linux
MySQL
EMail
Windows
Exchange
The Traditional Server Concept
• Pros
– Easy to conceptualize
– Fairly easy to deploy
– Easy to backup
– Virtually any
application/service can be
run from this type of setup
• Cons
– Expensive to acquire and
maintain hardware
– Not very scalable
– Difficult to replicate
– Redundancy is difficult to
implement
– Vulnerable to hardware
outages
– In many cases, processor is
under-utilized
The Virtual Server Concept
x86 Architecture
VMM (Virtual Machine Monitor)
Server
1
Guest OS
Server
2
Guest OS
Clustering
Service
Console
Intercepts hardware
requests
Terms
Host OS/Machine : It is the actual machine or OS on which
Virtualization takes place.
Guest OS/Machine : It is the actual Virtual machine or OS.
Hypervisor : he software or firmware that creates a virtual machine
on the host hardware.
Types of Virtualization
Full Virtualization
Para Virtualization
OS Virtualization
Hardware-baesd/ Full Virtualization
Full virtualization uses a special kind of software called a
hypervisor. The hypervisor interacts directly with the physical
server's CPU and disk space. It serves as a platform for the virtual
servers‘ operating systems. The hypervisor keeps each virtual
server completely independent and unaware of the other virtual
servers running on the physical machine. Each guest server runs on
its own OS -- you can even have one guest running on Linux and
another on Windows.
Example : VMWARE ESX
Full Virtualization
Host Machine
Guest OS Guest OS
Co-operative/Para-Virtualization
The para-virtualization approach is a little different than the full
virtualization technique, the guest servers in a para-virtualization
system are aware of one another. A para-virtualization hypervisor
doesn't need as much processing power to manage the guest
operating systems, because each OS is already aware of the
demands the other operating systems are placing on the physical
server. In para-virtualization the Host OS kernel act as Hypervisior
and is a link between hardware and guest OS.
Example : XEN Virtualization, Microsoft Hyper-V
Para-Virtualization
OS Based Virtualization
An OS-level virtualization approach doesn't use a hypervisor at all.
Instead, the virtualization capability is part of the host OS, which
performs all the functions of a fully virtualized hypervisor. The
biggest limitation of this approach is that all the guest servers must
run the same OS. Each virtual server remains independent from all
the others, but you can't mix and match operating systems among
them. Because all the guest operating systems must be the same,
this is called a homogeneous Environment
OS Based Virtualization
Limitations
For servers dedicated to applications with high demands on
processing power, virtualization isn't a good choice.
It's also unwise to overload a server's CPU by creating too many
virtual servers on one physical machine. The more virtual machines
a physical server must support, the less processing power each
server can receive.
Another limitation is migration. Right now, it's only possible to
migrate a virtual server from one physical machine to another if
both physical machines use the same manufacturer's processor
Virtualization Software
Microsoft Virtual PC
VmwareWorkstation
Vmware ESXi Server
Microsoft Hyper-V
Citrix XenServer
Oracle Virtual Box